1. Field of the Application
The present disclosure relates generally to a method and a system for controlling a combustion noise of diesel fuel and, more particularly, to a method and a system for controlling a combustion noise of diesel fuel to reduce a combustion noise of a diesel engine and improve fuel efficiency thereof by controlling injection parameters for the engine and a cylinder pressure level and adjusting a main injection timing with the use of a crank angle at a predetermined maximum heat release rate and a combustion noise index.
2. Description of the Related Art
As well known in the art, in the control of an internal combustion engine, a fuel injection mode changes in accordance with the operation conditions of the engine.
To this end, a main injection in the engine is preceded by a choice between a first injection mode, wherein a first pilot injection and a second pilot injection are conducted, and a second injection mode, wherein a main injection is conducted, in accordance with the engine operation conditions, and then fuel is injected in the selected injection mode.
Therefore, a change in a crank angle at an optimum heat release rate highly depends on the engine operation conditions, rather than showing a consistent pattern.
In particular, MFB50 (Mass Fraction Burned 50), a crank angle at which the heat release rate due to a combustion pressure reaches 50%, is used as a criterion for combustion control.
Meanwhile, open loop control has been widely used for the control of fuel injection in an engine. However, the method is giving place to closed loop control to calibrate emission, drivability and instability of engine operations resulting from variations in hardware.
Closed loop control involves setting target values of injection parameters by using a combustion pressure for an engine operating under the standard conditions (e.g. temperature and fuel status), obtaining measurement values of injection parameters for the combustion state of the engine in use in the same method used for determining the target value of injection parameters, calibrating a main injection timing during which fuel is injected into the engine in case that the target values and the measurement values of injection parameters are different, and stabilizing the engine combustion to the same level as under the standard conditions, thereby reducing exhaust gas.
To reduce exhaust gas, when the measurement values of injection parameters are retarded in comparison with the target values of injection parameters, the main injection timing is advanced to stabilize the engine combustion to the same level as under the standard conditions.
Meanwhile, in North America, where a cetane number varies in a wide range, manufacturers pursue fuel stability by using a cylinder pressure sensor. For this, they control the main injection timing of fuel into an engine to control a maximum combustion pressure regardless of a change in the cetane number.
Here, the existing configuration and system as above is based on a control logic to pursue combustion stability, whereas the present disclosure relates to a method and a system for controlling a combustion noise of diesel fuel, which employ the concept of a combustion noise index and reduce a combustion noise by controlling the pilot injection amount before the main fuel injection, rather than using the control logic as described above for fuel stability.
A Korean conventional art entitled “Fuel Injection Method for Decreasing Diesel Engine Combustion Noise” has been disclosed. However, the above disclosure is effective in that the reduction rate for a pressure increase slope of a combustion pressure (cylinder pressure) in a combustion chamber is surged by splitting the total amount of fuel to be injected into an engine into a pilot injection amount and a split injection amount, but has its limitations in that it does not disclose a technical idea, like that of the present disclosure, in which the concept of a combustion noise index is employed to control a pilot fuel injection amount by comparing with the preset target values of injection parameters.
The present disclosure illustrates and describes specific embodiments, but it will be obvious to those skilled in the art that the disclosure can be improved and modified in various ways within the technical spirit of the disclosure provided by the appended claims.